Thanks again for another reply.
Took a look at my motherboard last night and all of the caps look OK. I didn't notice any leaking or bulging. But as you say, my PC is pretty old so they might still be bad.
Was able to use the PC last night and used it without getting any reboots. Left it on all night just to see what would happen and because I wanted to try and seed some torrents and shred some old downloads. Made it through the night without any reboots. However, when I tried to download something else early this morning, it began to rev and I got hit with a reboot. Used safe mode to check the event log and there were a few more McAfee errors.
So, I'm gonna uninstall McAfee and check CNET for some freeware stuff to try out. If the problem is McAfee then I should find out soon enough I guess.
Any recommendations regarding some good freeware PC security software?